Investigation of the Cut-edge Protection Behavior of Zn-Al-Mg Coated Steel Sheets

摘要

Zinc coated steels are wildly used for the protection of steel structures from corrosion. Zn coated steel must be cut before use, creating an area where the bare steel substrate is exposed. Recently, it has been reported that the Zn coatings alloyed with magnesium show excellent cut-edge corrosion resistance, however the cut-edge corrosion mechanism of these coatings has not been well clarified. In this work, the cut-edge corrosion behavior of Zn-Mg-Al coated steel was investigated. The specimens were evaluated by the cyclic corrosion test and outdoor exposure test. The corrosion products of the coatings were analyzed with respect to the electrochemical and morphological stability. The morphology of cut-edge side after corrosion test revealed that the corrosion product of Zn-Mg-Al coated steel was more compact and dense than that of Zn coated steel. A potentiostatic test after the cut-edge corrosion test showed that the anodic current density at the cut-edge side of Zn-Mg-Al coated steel was lower than that of zinc coated steel. The corrosion product of Zn-Mg-Al coated steel was more stable and dense than that of zinc coated steel. All these results clearly suggest that magnesium assists the formation of compact and stable corrosion product and improves the cut-edge corrosion resistance of the Zn-Mg-Al coated steels.